<?php
error_reporting(0);
$a=$_POST['a'];  
$b=$_POST['b'];
if(preg_match('/cat|more|less|head|tac|tail|nl|od|vi|sort|cut|ping|curl|nc|grep|system|exec|bash|unique|find|popen|open|ls|rm|sleep|chr|ord|bin|hex|dict|#|`|\$|\<|\(|\[|\]|\{|\}|\)|\>|\_|\'|"|\*|;|\||&|\/|\\\\/is', $a)){
    die("hack!!!!");
}
if(!preg_match('/[a-z]/is', $b))
{
    die("big hack!!!!");
}
call_user_func($b,$a);